1. Field of the Invention:
The present invention relates generally to the field of jacks for lifting vehicles, and more specifically to a low profile jack which can lift a vehicle along a substantially vertical line, including a base frame having a base axle at a first end and a housing containing a hydraulic cylinder at a second end, a lift fork pivotally connected at a first end to the hydraulic cylinder through horizontal guide slots in the housing and having a cross bar at a second end to engage part of a vehicle to be lifted, a fulcrum fork half the length of the lift fork, pivotally connected at its first end to the base axle and at its second end to a lift axle extending laterally through the midsection of the lift fork, such that hydraulic pressure within the cylinder can push the first end of the lift fork along the guide slots and toward the first end of the fulcrum fork, thereby pivoting the lift fork so that its second end, together with the vehicle, move to a progressively higher position, the jack also including a brace fork for securing the lift fork second end at a certain elevation, the brace fork pivoting at a first end on the base axle so that the brace fork second end swings underneath the lift fork cross bar, and the lift fork can be lowered slightly to rest against retaining plates on the brace fork.
2. Description of the Prior Art:
There have long been jacks for lifting vehicles to execute repairs. Some of these have been bumper jacks which typically include a vertical rack member slid down into an opening in a base plate, and a rachet mechanism and lever for raising and lowering an attached bumper-engaging bracket. A problem with these jacks is that they tend to be unstable. A lateral force on the vehicle can cause the jack to tip over so that the vehicle falls, leading to crippling and sometimes fatal injuries. Assembly and disassembly of the bumper jack is typically a required inconvenience. Another common type of vehicle jack is the hydraulic floor jack. A horizontal hydraulic housing has a pump lever and a lift arm both pivoting from one end of the housing. A problem with this type of floor jack is that the arm rises along an arc, moving the vehicle or the jack horizontally during lifting. This movement creates dangerous instability and can cause harmful lateral loading on wheels supporting the elevated vehicle. Another problem is that the hydraulic housing must extend under the vehicle during use, but may not be low enough fit under some vehicles. Other jack variations have included the following.
Hunz, U.S. Pat. No. 2,361,690, issued on Oct. 31, 1944, discloses a jack for engaging and lifting part of a vehicle. A rachet carriage including a pawl and lever rides on a horizontal bar having teeth along its upper edge. A first linkage is pivotally connected to the carriage and to a vehicle engaging bracket. A pair of second linkages is pivotally connected to either side of the first linkage and to a base plate joined to an end of the horizontal bar. The carriage ratchets the lower end of the first linkage toward the lower ends of the second linkages, thereby progressively pivoting the first and second linkages into more vertical positions. This action in turn lifts the engaging bracket and vehicle. A reverse ratcheting action gradually lowers the bracket and vehicle. A problem with Hunz is that the relative geometric proportions of the first and second linkages and their connecting points do not create direct vertical lift. There is a dangerous and superfluous horizontal component of the lifting and lowering movements, similar to that described above for floor jacks.
Everson, U.S. Pat. No. 3,671,013, issued on Jun. 20, 1972, teaches a jack adapted for use in elevating the wings of a sail plane to support the plane during hanger storage. The structure includes two horizontal, parallel racks forming part of a base frame, and two arm members. An end of an arm member is pivotally connected to an end of each rack, and the other end of each arm member is joined to a contoured wing engaging plate. A pinion connected to one end of a lever member rides on each rack. The other end of the lever member pivotally connects to an arm. A winch mechanism drives the pinions along the racks to pivot the lever members and the arm members either upward or downward. The relative proportions of the Everson lever members, the arm members and the distances between pivot points bring about a lifting action with a horizontal component, as in Hunz.
Chiesa, U.S. Pat. No. 4,460,158, issued on Jul. 17, 1984, reveals a motorcycle and moped jack, A double arm member lift structure is pivotally connected to a base frame and is hinged upward by the action of a hydraulic cylinder and piston. Since the arm pivots from a translationally fixed fulcrum, the free ends of the arm members swing along an arc. Thus the lifting motion has both horizontal and vertical components.
Johnson, U.S. Pat. No. 3,659,824, issued on May 2, 1972, discloses an airplane jack. The lower ends of two arm members are pivotally mounted or: a horizontal rod. Two hydraulic cylinders are chained a lateral distance cut from the horizontal rod. The piston rods and cylinders are tilted upward to intersect and pivotally join to the upper ends of the arm members. Pumping the cylinders pivots the upper ends of the arm members upward to bear against and lift part of an airplane. Johnson lifts along an arc path just as Chiesa does.
Jarman, U.S. Pat. No. 4,690,378, issued on Sep. 1, 1987, teaches a vehicle jack including a horizontal rail with a lift arm pivotally connected at one end. A hydraulic cylinder at the other end of the rail drives a carriage along the rail. A lever is pivotally connected to the carriage and to the lift arm to pivot the lift arm upward and downward. Again, the lift arm has a translationally fixed fulcrum point and thus swings up and down along an arc, introducing a horizontal component into the lifting action.
It is thus an object of the present invention to provide a jack which is suitable for use in lifting objects and especially vehicles along a substantially vertical line for maximized stability and minimal shifting of the vehicle weight load. The avoidance of substantial horizontal movement during lifting is especially important for lifting race cars, where the load should not be shifted laterally to other wheels.
It is another object of the present invention to provide such a jack which collapses into a very low profile to easily fit under virtually any type of motor vehicle.
It is still another object of the present invention to provide such a jack which is sturdy and reliable.
It is finally an object of the present invention to provide such a jack which is relatively easy and inexpensive to manufacture.